Recent Findings on Road Salt in Maine’s Impaired Streams

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Recent Findings on Road Salt in Maines Impaired
Streams

• By Mark Whiting
• Maine DEP

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Discussion Topics

• Review of Penjajawoc Stream, Bangor ME
• Review of MDOT study from 30 years ago
• Why do we use road salt?
• What can be done?

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Chloride Medians for Penjajawoc Stream
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Stormwater BMPs

• Erosion Control
• Detention
• Infiltration
• Filtration
• CSOs
• Housecleaning
• There is no BMP treatment for salt!

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Why use road salt?

• Salts are cheap and effective de-icers.
• Maine has more people on the road, driving more
  hours, and yet road winter road fatalities are
  way down.
• Pre-treatment of roads with brine, esp. calcium
  or magnesium salts prevent ice from binding with
  the road surface.
• Ca and Mg salts are effective below 15º F
• Airports cannot use sand

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Why use road salt (continued)?

• Current winter road maintenance favors a bare
  road plan for all primary roads that allows
  people to travel faster. This has been
  successful while also reducing the number of
  accidents and fatalities. A bare road plan
  requires the use of salt. The amount of salt
  used for a given mile of road has been increasing
  nationwide.

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From Margaret Chase Smith Policy Center Report
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Sources of Salt in Surface and Groundwater

• Natural sources, atmospheric deposition of ocean
  aerosols, decomposition of organic matter
• Road salt, in Maine there was about 490,000
  tons/yr for 2008-2009, 21 tons/mile of road
• Landfills and organic debris
• Water softeners

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From NH DES TMDL Study
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From NH TMDL Study
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From Margaret Chase Smith Policy Center Report
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Problems from Salt

• Sodium is a nutrient, but too much is bad.
  Drinking water standard is 250 mg/L, but 20 mg/L
  is the limit for people with salt restricted
  diets.
• Chloride is not a nutrient, but it is abundant in
  body fluids. The Maine Aquatic Life standard is
  230 mg/L for chronic exposures ( 4 days).
• Salts acidify soils and leach nutrients from
  soils and from plant tissues, decrease surface
  water alkalinity by leaching away cations (esp.
  Ca Mg)
• Lakes can develop haloclines that trap nutrients
• Corrosion of metals (esp. cars and bridges) and
  damage to road surfaces (esp. concrete)

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Season is important

• Most groundwater recharge occurs in the late
  winter and early spring associated with spring
  melts. These conditions also mobilize salts.
• Spring melts strongly affect surface runoff too.
  Peak conductivity generally occurs from Feb to
  April during these thaws.

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Summary of Peak Observed Chloride Concentrations
(from Environment Canada)
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Long-term trends

• Background Cl concentrations are probably about
  20-30 mg/L for Atlantic states, the Canadian
  shield provinces have some of the lowest 1-5 mg/L
• Salt concentrations are increasing in
  groundwater, soils, and surface water in all
  northern states and Canada.

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BMPs for better water quality

• Dont use more salt than you need, and use modern
  mixes.
• Application strategies, salt mixes, pre-wetting,
  pre-application of brine using Ca or Mg salts,
  weather sensors, bridges my have built in
  applicators (MN, ON).
• Better road designs, better tires.
• Sand only applications (parking lots?)
• Stay home in bad weather.

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BMPs for Better Water Quality

• Apply at the right place (i.e., hills, curves,
  bridges and shaded patches of road need special
  attention)
• Apply at the right time (i.e., as early as
  possible, prevention works better than reaction,
  anti-icers applications can work for days and
  prevent ice from bonding with the road)
• Factor in expected traffic volume, day/night
  temperature changes, etc.

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More BMPs

• Salt storage areas need to be covered
• Snow dumps must be remote from sensitive
  locations
• Use green deicers such as organic salts, i.e.,
  calcium magnesium acetate, potassium acetate,
  sodium acetate
• Low salt techniques can save money and improve
  public safety